Carl Felland
The Pennsylvania State University

A biofix is a biological marker that initiates the beginning of degree-day calculations. For insects, it is usually the date of a particular pest event, such as moth flight in the spring. The timing of a pest event in the spring depends on the weather history since the previous fall. Consequently, some measure of the historical weather conditions can help us time the placement of traps in order to determine pest biofixes for a particular orchard. This measures degree days (DD), more importantly their addition over time as accumulated degree days (ADD). On the IPM Apple Insect product, we chose a "base" of 43 F to calculate daily degree days. This base allows us to monitor even the earliest appearing insects in the spring. Accumulated degree days accounts for the addition of heat to the environment as the days begin to warm in early spring. This addition or accumulation of heat is directly related to insect activity. By computing accumulated degree days (ADD) and correlating them to past insect events, we can estimate the likely flight or hatch of some particular pest.

The accumulated degree days (ADD) base 43 F from January 1 will help you identify the best time for placing traps to determine your local biofixes. Where trapping data is not available, they can be used to approximate biofixes based on other sites and species. You can replace the ADD-estimated biofixes with trap values by simply calling in your observed biofix dates to SkyBit's toll-free number at 1-800-454-2266. The estimated and observed biofix dates are reported in the IPM product under the appropriate species header.

A couple of notes concerning the trapping of insects to determine biofix dates. Biofixes are not usually identified with the first capture of a pest in the early season. We prefer to use a "sustained capture."  A sustained capture is determined either by several individuals being captured per trap (i.e., 5 moths in 3 traps), resumption of capture followed by extended period without capture, or by "back-calculating" using observations from a later development stage. The use of sustained capture for the biofix eliminates false starts due to fluctuating temperatures early in a season that are conducive for flight but do not support mating and egg-laying.